The Succulent Karoo’s natural wonders

The high diversity of dwarf-leaf succulents is the most distinctive characteristic of the Succulent Karoo, with vygies being the most numerous and prominent, writes Cameron McMaster.?
Issue date : 21 November 2008

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Cameron McMaster

The Succulent Karoo is an arid semi-desert region extending in an interrupted belt from southern Namibia through the Richtersveld and Namaqualand, the Knersvlakte, the Bokkeveld, the Tanqua and Robertson Karoos and eastward in narrow bands into the rain-shadow areas of the Little Karoo as far as Willowmore and Steytlerville in the Eastern Cape. I t’s the fourth largest biome after the Savanna, Nama Karoo and Grassland biomes. It has developed as a result of a unique set of climatic and environmental conditions, primarily a result of low precipitation in winter.

The rainfall in the western part is very low, below 100mm along the Namaqualand coast, and it seldom exceeds 200mm/year, but the rain is dependable and prolonged droughts are rare. Due to the influence of the cold Benguela current, up the West Coast, there are frequent mists that roll in from the sea. These have a cooling effect and augment rainfall along the Namaqualand coast and west-facing escarpments. The geology is complex, giving rise to a wide variety of soil types and altitudinal ranges. However, due to the low rainfall there has been little leaching and the soils are generally neutral to alkaline and well supplied with mineral and trace elements. The soils also possess special features that modify water infiltration, subsurface storage and water supply to plants.

Climatic conditions have forced the plants to evolve a number of strategies to survive, either by developing water-storage capabilities or by adopting extremely short life cycles completed within one growing season. T he high diversity of dwarf-leaf succulents is Succulent Karoo’s most distinctive characteristic, with vygies, members of the Aizoaceae family, being the most numerous and prominent. Members of almost all the plant families including Euphorbiaceae, Crassulaceae, Hyacinthaceae and Asteraceae have developed some form of succulence. Some species have developed bizarre shapes, like stones.

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Others bury themselves in soil to minimise water loss, absorbing sunlight for photosynthesis through transparent windows at soil level, such as Lithops. There are no less than 1 600 succulent species in this biome, an amazing 16% of the world’s estimated 10 000 succulents. Plants that have developed bulbs as storage organs are collectively referred to as geophytes, another successful diversity, and these comprise no less than 18% of the flora. It’s said the most prolific bulbous flora on earth occurs here, with many species of spectacular beauty.

The bulb capital he Bokkeveld in the Nieuwoudtville area are reputed to have more bulbous plants per square metre of soil than anywhere else, giving it the reputation of the bulb capital of the world. Bulbous plants occupy every conceivable niche in the environment and have developed special leaf forms to catch the maximum amount of moisture from periodic fog and nightly dew. he vast number of annual plants, such as daisies, germinate, flower and set seed in the space of a few months, a process that has been going on for millions of years. In all species seed development depends on the successful pollination of each flower, the sole function of which is to attract pollinators.

The ecosystem involves not only plants, but a huge diversity of special insects, animals and reptiles – all interdependent. he Succulent Karoo provides us with the most spectacular floral display on earth, attracting thousands of tourists and making it important to the economy of the region. It’s estimated the Succulent Karoo is home to over 6 000 species of vascular plants in over 1 000 genera and 170 families. An amazing 26% of these are endemics occurring nowhere else and a further 14% are near-endemics that have the centre of their distribution in this biome. Most of the 80 genera endemic to the biome are either succulents or geophytes.

Man’s footprint Sadly, changing land use patterns and the footprint of man have resulted in rapid degeneration, with the result that many very specialised and sensitive plants are threatened by loss of habitat and destruction by commercial agriculture and livestock production. There has been ongoing poaching of wild succulent plants by collectors and heavy exploitation of species such as ghaap (Hoodia gordonii). It has almost been wiped out in large tracts of the Tanqua Karoo for use in the slimming industry. Of all Succulent Karoo species, 17% are listed as Red Data Species, rare and threatened and in dire need of conservation. Only 6% of the biome is formally protected in reserves such as the Tanqua Karoo and the Richtersveld National Park and these don’t cover all the different features and veld types within the region.

The Richtersveld is absolutely unique in terms of geology and botanical riches. Although a national park it’s occupied by an indigenous community who aren’t yet fully aware of the vital role they play in biodiversity conservation, which could be an income source far exceeding destructive livestock farming. It’s a matter of concern to hear reports from visitors to the Richtersveld of ongoing and increasing degradation of the environment, not only by livestock but also by increasing mining activity. Ironically, large tracts of land under concession to mining companies in the Alexander Bay area have up to now been protected from overgrazing and remained pristine. This has now been altered by the award of a land claim over the area and deterioration seems inevitable. It’s hoped the community will be guided to adequate conservation. Those privileged to own or occupy land in this special region have a responsibility to ensure it’s conserved for future generations. Contact Cameron McMaster at [email protected]. |fw